Drs Brian Lacy And Kishore Iyer Discuss Short Bowel Syndrome - Part 1

How is short bowel syndrome different than chronic intestinal failure? How do we best diagnose short bowel syndrome? What are some of the potential complications to be aware of and how do we avoid them? Drs Brian Lacy and Kishore Iyer discuss all these important questions and more on part 1 of this 2-part podcast.

Brian Lacy, MD, is a professor of medicine and gastroenterologist at the Mayo Clinic in Jacksonville, Florida. Kishore Iyer, MD, is a professor of surgery and pediatrics and director of the Intestinal Rehabilitation & Transplant program at Mount Sinai Hospital in New York City, New York.

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Transcript:

Dr. Brian Lacy:
Welcome to Gut Check, a podcast from the Gastroenterology Learning Network. My name is Brian Lacy. I'm a Professor of Medicine at the Mayo Clinic in Jacksonville, Florida, and I'm absolutely delighted to be speaking today with Dr. Kishore Iyer, Professor of Surgery and Pediatrics and a member of the Intestinal Rehabilitation and Transplant Program at Mount Sinai Hospital in New York City.

Dr. Iyer is an expert in the evaluation and management of patients with chronic intestinal failure. Our topic today, short bowel syndrome, is one that is so incredibly important to patients with this life-altering disorder and also so very important to the gastroenterologists and surgeons and dieticians who evaluate these patients.

So Dr. Iyer, welcome. To begin our discussion today and to kind of set the stage for our listeners, could you provide a clear definition of short bowel syndrome? Is the only factor the length of small intestine remaining, or do patients have to have symptoms, as well? And do we factor in nutritional issues?

Dr. Kishore Iyer:
Thank you, Dr. Lacy, for the introduction and for inviting me to this podcast on a subject that's very dear to my heart. So coming right to the question, the definition of short bowel syndrome really relates strictly to residual bowel length. The generally accepted definition for short bowel syndrome refers to residual bowel length of 200 centimeters or less, though there is a move toward suggesting that that is a little generous, and a stricter criterion would suggest that 150 centimeters of residual small bowel would define somebody as having short bowel. And just to be very clear, this refers only to residual small intestinal length.

Brian Lacy:
So we don't really factor in symptoms, and we don't factor in nutritional issues. Is that correct?

Dr. Kishore Iyer:
That is an important question. The definition of short bowel, as I said, again, strictly refers to length, without reference to symptoms or needs for additional therapy. And the common confusion or source of confusion relates to sometimes the term being used interchangeably with intestinal failure, and we can talk a little more about that. But intestinal failure brings in functional consequences of the underlying disease, which in the majority is short bowel syndrome, but there may be other causes of intestinal failure.

Dr. Brian Lacy:
So that's wonderful, Dr. Iyer. Perfect segue, because I think there is some confusion about those two terms. Are they equal? Are they analogous? But it sounds like there are some important differences, and would you highlight, maybe, some of those important differences? Is chronic intestinal failure just a more severe form of short bowel syndrome?

Dr. Kishore Iyer:
That's interesting. The definition of chronic intestinal failure is the one published by Loris Pironi, a colleague from the ESPEN Holland group. And I'm going to paraphrase here, but chronic intestinal failure refers to the loss of intestinal function, to the extent that intravenous supplementation, often in the form of parenteral nutrition, becomes required. And there's the functional implication. Now, in the majority of cases, chronic intestinal failure is caused by anatomic loss of small bowel length, which we already alluded to a short bowel syndrome. So short bowel syndrome is the cause of chronic intestinal failure in about 60 to 70% of cases. That's also telling us that in the remainder 20 to 30% of cases chronic intestinal failure may be caused by functional disorders in the intestine i.e., where gut length is not the problem, functionally the residual intestine is the problem.

Dr. Brian Lacy:
So how common is short bowel syndrome?

Dr. Kishore Iyer:
Perhaps the right question is how uncommon is short bowel syndrome? It is indeed very uncommon. It meets the criteria for orphan disease in the United States. The estimated prevalence ranges widely. There's poor data in this regard, but we now believe that the estimated prevalence in the US is about somewhere between 25,000 to 40,000 patients. And that probably more accurately refers to the prevalence of intestinal failure. So the actual prevalence of short bowel syndrome likely to be a subset of the whole is probably somewhere around 15,000 patients. The NIH would say one to three per million of the population. It is likely that that's an underestimate, but I've already suggested in more ways than one that we actually may not even know the true prevalence other than knowing that it's quite uncommon.

Dr. Brian Lacy:
And so if we think about this disorder, what are some of the most common risk factors for developing short bowel syndrome?

Dr. Kishore Iyer:
So short bowel syndrome relates to anatomic loss of length. And when I'm talking to people, I like to start with two illustrative examples at the extreme. You could have a previously well adult patient, and for the moment I'm going to speak only about adults. You could have an adult patient who was perfectly well for perhaps the first 30, 40 years of his life, suddenly develops a blood clot to his intestine, what we call a centric thrombus or an embolus from somewhere else, perhaps has underlying cardiac disease with atrial fibrillation, throws off a plaque to his mesenteric artery and almost in one fell instant, loses the blood supply to his intestine, loses all of his intestine. That's catastrophic short bowel syndrome occurring immediately. At the other extreme, and gastroenterologists will recognize this very well, is the patient with Crohn's disease spanning perhaps many decades, several surgical resections with surgical attempts of being conservative with resection bowel, but ultimately gradually with worsening malabsorption. Suddenly one day the patient's not doing well and you look back and you realize now we have a patient with short bowel syndrome.

Between those two extremes of several etiologies, the common causes I've already alluded to, mesenteric ischemia, Crohn's disease, and then sadly there is surgical misadventure. Misadventure, I use the term broadly and loosely, but patients who have an ease of obstructions, multiple difficult operations resulting in loss of bowel. Then there is trauma in enlarged metropolitan area like in New York, gunshot wounds for example. These are the common causes of short bowel syndrome in adult patients. Just to touch on this issue for children, congenital causes of loss of bowel obviously become an important cause. Midgut volvulus, for example, gastroschisis for example, and events in the perinatal period such as necrotizing enterocolitis leading to loss of bowel length.

Dr. Brian Lacy:
What's the most accurate way to diagnosis? Can we just rely on surgical records for a measure of how much small bowel is remaining, although sometimes those records are 30 to 40 years old, or do we need imaging studies? Can we trust a simple small bowel follow through or MR enterography?

Dr. Kishore Iyer:
Unfortunately we know that surgical records, a good surgical record is the most accurate way to get a residual small bowel length. Woefully, most surgeons were not thinking of short bowel, only tell us what they removed. They do not tell us what was left behind. And I tell patients and colleagues, bowel that was removed is no use to man or beast. What the clinician needs is the residual bowel. So the best estimate for residual bowel length is carefully measured at the time of surgery. And there's a convention to this. I use a piece of thread, a piece of silk suture along the antimesenteric border of unstretched bowel from the duodenojejunal flexure to the ileocolic junction or the site of any distal anastomosis or distoma. That is the most accurate measure of residual bowel.

Now there have been reports, there's a famous paper now almost of historic value from Jeremy Nightingale in the UK that suggested you could accurately measure bowel length using well performed small bowel contrast studies. They used a device called the episiometer, which is used to measure distances on maps and they used that to measure bowel length. We've shown that these are unreliable and they sometimes absent good surgical data, we rely on contrast studies. I still prefer the conventional contrast mobile series, but absent these things we do the best we can. If I may make one more plea to your audience, if you are in the business of looking after these patients, please either you report or get your surgeon to report residual bowel length, carefully measured at operation.

Dr. Brian Lacy:
Wonderful. Hopefully we can change practice moving ahead, not record what was removed, but instead record what is left. So thinking about the patient with short bowel syndrome, do symptoms develop solely due to rapid transfer through the short and length of small bowel or other factors are at play?

Dr. Kishore Iyer:
That's a great question. It's a difficult question. Certainly the dominant underlying problem simply and when we focus on length, and I don't want to expand on that, but really what is happening is loss of absorptive surface area. So certainly the overriding symptoms of diarrhea or increased ostomy output and GI losses refer really to loss of length and perhaps more importantly loss of absorptive surface area. But really alongside this comes additional symptoms related to malabsorption related to rapid transit, GI discomfort, abdominal pain, sometimes periods of abdominal distension, inability to tolerate a big meal. And you can imagine the rest. So most of the symptoms do relate to loss of length, but there can be additional symptoms that might relate to related pathology or to associated complications.

Dr. Brian Lacy:
Thinking about some of these complications, can you list some of the most common complications we might anticipate?

Dr. Kishore Iyer:
These can mostly be determined on a first principles basis. If we say loss of absorptive surface area is the primary problem, diarrhea or increased GI losses is the attendant first result. Now, unrecognized diarrhea, improperly inadequately managed diarrhea or inadequately managed trauma losses result in dehydration and its downstream consequences such as acute dehydration, acute kidney injury. Unfortunately in my practice I see a lot of patients presenting for the first time with intestinal failure and I'm deliberately using the term intestinal failure rather than short bowel. But with intestinal failure or short bowel who have for the first time who have underrecognized or unrecognized subclinical kidney injury likely arising as a consequence of unrecognized diarrhea and appropriate repletion. So there's a preventable complication of the short bowel syndrome. Other things, weight loss, features of malnutrition, malnutrition related both to macronutrient depletion and indeed to micronutrients, skin abnormalities, loss of hair, nail problems.

And then there are the more obscure but well recognized complications in select patients with short bowel. For example, depending on the anatomic region of the bowel that is lost, you can almost predict what is likely to happen. So the patient who has terminal ileal resection with retained jejunum is likely to have B12 efficiency and a predictable macrocytic anemia. The patient who has a high jejunostomy alongside lost his ileum B12 deficiency, but likely to have an overall hyper secretory state and be prone to diarrhea.

In contrast, the patient, let's say with residual jejunum, a small limited amount of residual jejunum with retained colon is at risk for kidney stones and kidney stones primarily related to hyperoxaluria and oxylate stones. And the pathology pathophysiology is really quite obvious if only we think about it, right? Unbound oxylate delivered to the colon, converted to oxylate iron is absorbed leading to hyperoxaluria and a good screening technique to do is to check for serum oxylate or oxylate in the urine. So correction of hyperoxaluria and prevention of oxylate stones in the patient with short bowel who has retained colon is really to ensure delivery of adequate calcium in the GI lumen. Don't be guided by serum calcium. You need luminal calcium to bind unbound oxylate. I tell patients to take Tums every day and you'll thank me for it.

Dr. Brian Lacy:
Thank you. That's wonderful. Great review of physiology and complications. Now, before we jump ahead to discussing treatment, you wrote a really interesting article highlighting kind of an overall lack of awareness about short bowel syndrome and chronic intestinal failure. Could you just comment on that for our listeners?

Dr. Kishore Iyer:
Absolutely. Dr. Lacy. And this is a recent pivot of mine. After doing 20 years of surgery and transplant, I've pivoted to health systems research and I tell people as I peel each successive layer of the intestinal failure onion, I'm forced to cry ever more. Because I think what has happened with intestinal failure care in the United States is the perfect trifecta of a rare disease, lack of expertise and decentralization. So we have a rare and complex disease. Now we are speaking about short bowel, so referring to short bowel, a really rare and predictably complex disease that requires complex therapies. If you think of a population prevalence of two three per million, you could easily imagine even busy gastroenterologists going through several years of their practice not encountering one such patient. There are many states in the union unfortunately, that do not have good multidisciplinary expertise in intestinal failure.

And this is a very serious problem. These patients often go from pillar to post trying to find centers that can look after them, and Dr. Montre Mundi, David Mercer and I were involved with a group that recently published on looking at the characteristics of intestinal failure across the United States on the basis of a large third party claims database analysis. And what we found was really quite disheartening that patients have to travel very long distances for their care or in further work we are now understanding they really get suboptimal care.

One of the things we've done, if I may make a pitch here, is to try and address that problem of launched in online learning platform called the LIST-ECHO Project, learn Intestinal Failure TeleECHO, and it runs as a twice a month for adults, one-hour session each time. It's an online Zoom based it's based on the very popular ECHO platform from Dr. Sanjeev Arora in New Mexico. And this is now applied to intestinal failure. We have people sign in at this point in time from six of seven continents. They present an anonymized case, I facilitate discussion and we have a collection of didactics now about 75 or so archived on our website, all at no cost and we provide free CME. Thank you for allowing me to make that pitch.

Dr. Brian Lacy:
Wonderful. This is an educational podcast, so this is great. So for our listeners today, if interested, the Lift Echo Project, Google that, and you'll get plugged in.

Be sure to join us for part two of this podcast as Drs Lacy and Iyer discuss treatment options for patients with short bowel syndrome.